Digital signal: strong anti-interference ability and good communication confidentiality.

Digital signal, as its name implies, is that the independent variable is discrete and the dependent variable is also discrete. The independent variable of digital signal is represented by integer, and the dependent variable is represented by finite number. Digital signals are represented by two physical states: 0 and 1, so the quality of digital signals is very strong and the anti-interference ability is relatively strong.

Analog signal refers to a signal whose information parameters are continuous within a given range. The characteristic quantity of analog signal information can be instantly converted into any digital signal. In the transmission process of analog signals, it is necessary to convert information signals into radio signals, and then transmit them by wired or wireless means.

Disadvantages of analog signals:

Poor confidentiality of analog signals: analog communication, especially microwave communication and wired communication, is easy to be eavesdropped. As long as the analog signal is received, it is easy to get the communication content.

Weak anti-interference ability of analog signals: electrical signals will be interfered by various noises inside and outside the communication system during transmission along the line, and it is difficult to separate the noise from the signal after mixing, thus reducing the communication quality. The longer the line, the more noise is accumulated.

Digital signal has strong anti-interference ability;

Digital signals will be mixed with noise during transmission. The input signal voltage can be measured by mosfet (called threshold) composed of electronic circuits. Only when the voltage reaches a certain amplitude, the circuit will have an output value and automatically generate neat pulses (called shaping or regeneration). When the small noise voltage comes, it will be filtered out because it is lower than the threshold value, and it will not cause circuit action. Therefore, the regenerated signal is exactly the same as the original signal, and only when the interference signal is greater than the original signal will an error code be generated. In order to prevent the error code, the method of error detection and correction is set in the circuit, that is, when the error code occurs, the opposite party can be retransmitted by using the reverse signal. Therefore, digital transmission is suitable for long-distance transmission and lines with poor performance.

Advantages of digital signals:

Digital signals enhance the confidentiality of communication: after A/D conversion, digital voice signals can be encrypted first, then transmitted, decrypted at the receiving end, and then restored to analog signals through D/A conversion. Digitalization of speech provides a very favorable condition for encryption processing. The more password digits, the more difficult it is to decipher.

A signal is a physical quantity representing information. For example, electrical signals can represent different information through changes in amplitude, frequency and phase. This kind of electric signal can be divided into analog signal and digital signal. Signals are tools and carriers of information. Broadly speaking, it includes optical signals, acoustic signals and electrical signals. According to practical use, signals include TV signals, broadcast signals, radar signals, communication signals and so on. According to the time characteristics, there are deterministic signals and stochastic signals.

Signals are tools and carriers of information. Broadly speaking, it includes optical signals, acoustic signals and electrical signals. For example, the ancients used the rolling wolf smoke generated by lighting beacon towers to convey the news of enemy invasion to distant troops, which belongs to optical signals; When we speak, sound waves reach other people's ears to make them understand our intentions, which belongs to acoustic signals;

All kinds of radio waves propagating in space and currents extending in all directions in the telephone network can be used to express all kinds of messages to the distance, which belong to electrical signals. Only by receiving light, sound and electrical signals can people know what the other party wants to express.